The present invention relates to rolls which can be used in calenders and analogous machines to treat running webs or sheets of paper, textile material, plastic foil and the like. The invention also relates to assemblies of rolls which can be used in such machines and wherein at least one roll has a floating shell which surrounds a stationary carrier.
It is known to provide a calender roll with a flexible hollow cylindrical shell which floats on one or more rows of hydrostatic bearing elements supported by a stationary beam-like carrier and defines with an adjacent roll an elongated nip for the running web. The hydrostatic bearing elements receive pressurized fluid from a regulating unit whose operation is controlled by signals denoting the pressures at various locations along the nip. As a rule, each bearing element comprises at least one pressure transmitting unit having a plunger which defines with the carrier (or with a part on the carrier) a cylinder chamber receiving pressurized hydraulic fluid from a regulator and communicating with an external pocket of the plunger by a flow restricting passage. Pressurized fluid which enters the pocket leaks along the internal surface of the shell and prevents the shell from coming into direct metal-to-metal contact with the plunger. The forces which are generated by such pressure transmitting units are directed toward the nip, and the pressure of hydraulic fluid which flows into the cylinder chambers of discrete pressure transmitting units, into the cylinder chambers of several pressure transmitting units in a given bearing element, or into the cylinder chambers of one or more pressure transmitting units in two or more bearing elements is regulatable individually so as to allow for the establishment of a predetermined pattern of pressures along the nip.
It is also known to equip a roll of the just outlined character with means for regulating the temperature of the hydraulic fluid, i.e., for withdrawing heat or for admitting heat, depending on the monitored temperature of such fluid. It is further known to regulate the quantity of heat which is transmitted between the shell and the pressurized hydraulic fluid. Reference may be had to German Offenlegungsschrift No. 24 20 324 which discloses a roll that is particularly suited for the treatment of running paper webs in calenders and like machines. The roll comprises a row of hydrostatic bearing elements which are mounted on the carrier opposite the nip for the paper web. Groups of neighboring bearing elements receive pressurized hydraulic fluid by way of common conduits which, in turn, receive pressurized fluid from adjustable valves in the regulating unit. The pressure of fluid streams flowing through the valves is regulated with a view to establish a desired distribution of pressures along the nip. The entire body of hydraulic fluid is heated in a heat exchanger and each conduit contains an auxiliary heater which renders it possible to alter the temperature of fluid flowing to the corresponding group of bearing elements. The auxiliary heaters contribute to the complexity as well as to the initial and maintenance cost of the roll. Moreover, the ability of the auxiliary heaters to influence the temperature of the roll is rather limited because a synthetic oil cannot be heated beyond 240.degree. C. and the quantity of oil which can be delivered to the bearing elements per unit of time is limited by the pressure regulating unit whose primary function is to select the pressure along the nip.
German Pat. No. 25 03 051 discloses a roll wherein the heating action upon the shell is independent of the pressure regulating action, i.e., of the supporting action of bearing elements upon the shell. In accordance with the teaching of this patent, the carrier supports an additional set of (secondary) bearing elements which are mounted diametrically opposite the (primary) bearing elements for regulation of the pressure along the nip and receive a suitable heating fluid which is to influence the temperature of the shell. The secondary bearing elements are similar to the primary bearing elements and the heating fluid which is fed to the secondary bearing elements is or can be identical with the fluid which is supplied to the primary bearing elements. The main difference is that the fluid which is supplied to the secondary bearing elements is maintained at a different pressure as well as at a different temperature. Moreover, the mutual spacing of secondary bearing elements is greater than that of the primary bearing elements.
Commonly owned U.S. Pat. No. 4,520,723 to Pav et al. discloses a roll wherein a rotary flexible shell surrounds a stationary carrier and a set of primary bearing elements is used jointly with a set of secondary bearing elements which are offset with reference to the primary bearing elements in the circumferential direction of the shell. At least one component of force which is generated by each primary bearing elements acts counter to the direction of the force which is applied to the shell in the nip of such shell with a second roll. The forces which are generated by the secondary bearing elements have components acting counter to the action of forces which are generated by the primary bearing elements, i.e., in the direction of the force acting in the nip and tending to move the corresponding portion of the shell nearer to its carrier. If each of the primary and secondary bearing elements comprises a pair of neighboring pressure transmitting units (note, for example, FIG. 2 of Pav et al.), each such bearing element further generates a force acting transversely of the direction of action of the aforediscussed components, i.e., at right angles to a plane including the axis of the roll and the nip which the shell of such roll defines with a neighboring roll. The patented arrangement entails a desirable stabilization of the shell by preventing it from yielding to externally applied transverse forces.
Commonly owned U.S. Pat. No. 4,394,793 discloses a roll with hydrostatic bearing elements each of which comprises two pressure transmitting units. German Pat. No. 29 02 956 discloses a roll with several heaters for the hydraulic fluid. Commonly owned U.S. Pat. No. 4,328,744 discloses rolls wherein each primary and each secondary bearing element can comprise two or more pressure transmitting units.